I have a P4 that was only flown 4 times before it went into storage for 3 years. All 3 of my batteries have the exact same symptoms: Touch the button once - 1 LED. Attempt to turn on - won't turn on, but all lights come on briefly. Do the 5-seconds down battery life check - all LEDs. Put it on charger - LED 1 flashes fast with Button light on, then both lights off for a few seconds, repeat. I've tried this for hours with all 3 batteries, no change.
From this thread, and others like it I've researched, it seems that they're all so depleted that there's nothing I can do, but buy new batteries? Seems odd that they'd all be doing the same thing and there's no hope for any of them...
Thanks,
Mark